arm64: kgdb: Fix single-step exception handling oops

[linux/fpc-iii.git] / fs / xfs / xfs_reflink.c

/*
 * Copyright (C) 2016 Oracle.  All Rights Reserved.
 *
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_defer.h"
#include "xfs_da_format.h"
#include "xfs_da_btree.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_inode_item.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_error.h"
#include "xfs_dir2.h"
#include "xfs_dir2_priv.h"
#include "xfs_ioctl.h"
#include "xfs_trace.h"
#include "xfs_log.h"
#include "xfs_icache.h"
#include "xfs_pnfs.h"
#include "xfs_btree.h"
#include "xfs_refcount_btree.h"
#include "xfs_refcount.h"
#include "xfs_bmap_btree.h"
#include "xfs_trans_space.h"
#include "xfs_bit.h"
#include "xfs_alloc.h"
#include "xfs_quota_defs.h"
#include "xfs_quota.h"
#include "xfs_btree.h"
#include "xfs_bmap_btree.h"
#include "xfs_reflink.h"
#include "xfs_iomap.h"
#include "xfs_rmap_btree.h"
#include "xfs_sb.h"
#include "xfs_ag_resv.h"

/*
 * Copy on Write of Shared Blocks
 *
 * XFS must preserve "the usual" file semantics even when two files share
 * the same physical blocks.  This means that a write to one file must not
 * alter the blocks in a different file; the way that we'll do that is
 * through the use of a copy-on-write mechanism.  At a high level, that
 * means that when we want to write to a shared block, we allocate a new
 * block, write the data to the new block, and if that succeeds we map the
 * new block into the file.
 *
 * XFS provides a "delayed allocation" mechanism that defers the allocation
 * of disk blocks to dirty-but-not-yet-mapped file blocks as long as
 * possible.  This reduces fragmentation by enabling the filesystem to ask
 * for bigger chunks less often, which is exactly what we want for CoW.
 *
 * The delalloc mechanism begins when the kernel wants to make a block
 * writable (write_begin or page_mkwrite).  If the offset is not mapped, we
 * create a delalloc mapping, which is a regular in-core extent, but without
 * a real startblock.  (For delalloc mappings, the startblock encodes both
 * a flag that this is a delalloc mapping, and a worst-case estimate of how
 * many blocks might be required to put the mapping into the BMBT.)  delalloc
 * mappings are a reservation against the free space in the filesystem;
 * adjacent mappings can also be combined into fewer larger mappings.
 *
 * As an optimization, the CoW extent size hint (cowextsz) creates
 * outsized aligned delalloc reservations in the hope of landing out of
 * order nearby CoW writes in a single extent on disk, thereby reducing
 * fragmentation and improving future performance.
 *
 * D: --RRRRRRSSSRRRRRRRR--- (data fork)
 * C: ------DDDDDDD--------- (CoW fork)
 *
 * When dirty pages are being written out (typically in writepage), the
 * delalloc reservations are converted into unwritten mappings by
 * allocating blocks and replacing the delalloc mapping with real ones.
 * A delalloc mapping can be replaced by several unwritten ones if the
 * free space is fragmented.
 *
 * D: --RRRRRRSSSRRRRRRRR---
 * C: ------UUUUUUU---------
 *
 * We want to adapt the delalloc mechanism for copy-on-write, since the
 * write paths are similar.  The first two steps (creating the reservation
 * and allocating the blocks) are exactly the same as delalloc except that
 * the mappings must be stored in a separate CoW fork because we do not want
 * to disturb the mapping in the data fork until we're sure that the write
 * succeeded.  IO completion in this case is the process of removing the old
 * mapping from the data fork and moving the new mapping from the CoW fork to
 * the data fork.  This will be discussed shortly.
 *
 * For now, unaligned directio writes will be bounced back to the page cache.
 * Block-aligned directio writes will use the same mechanism as buffered
 * writes.
 *
 * Just prior to submitting the actual disk write requests, we convert
 * the extents representing the range of the file actually being written
 * (as opposed to extra pieces created for the cowextsize hint) to real
 * extents.  This will become important in the next step:
 *
 * D: --RRRRRRSSSRRRRRRRR---
 * C: ------UUrrUUU---------
 *
 * CoW remapping must be done after the data block write completes,
 * because we don't want to destroy the old data fork map until we're sure
 * the new block has been written.  Since the new mappings are kept in a
 * separate fork, we can simply iterate these mappings to find the ones
 * that cover the file blocks that we just CoW'd.  For each extent, simply
 * unmap the corresponding range in the data fork, map the new range into
 * the data fork, and remove the extent from the CoW fork.  Because of
 * the presence of the cowextsize hint, however, we must be careful
 * only to remap the blocks that we've actually written out --  we must
 * never remap delalloc reservations nor CoW staging blocks that have
 * yet to be written.  This corresponds exactly to the real extents in
 * the CoW fork:
 *
 * D: --RRRRRRrrSRRRRRRRR---
 * C: ------UU--UUU---------
 *
 * Since the remapping operation can be applied to an arbitrary file
 * range, we record the need for the remap step as a flag in the ioend
 * instead of declaring a new IO type.  This is required for direct io
 * because we only have ioend for the whole dio, and we have to be able to
 * remember the presence of unwritten blocks and CoW blocks with a single
 * ioend structure.  Better yet, the more ground we can cover with one
 * ioend, the better.
 */

/*
 * Given an AG extent, find the lowest-numbered run of shared blocks
 * within that range and return the range in fbno/flen.  If
 * find_end_of_shared is true, return the longest contiguous extent of
 * shared blocks.  If there are no shared extents, fbno and flen will
 * be set to NULLAGBLOCK and 0, respectively.
 */
int
xfs_reflink_find_shared(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           agbno,
        xfs_extlen_t            aglen,
        xfs_agblock_t           *fbno,
        xfs_extlen_t            *flen,
        bool                    find_end_of_shared)
{
        struct xfs_buf          *agbp;
        struct xfs_btree_cur    *cur;
        int                     error;

        error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp);
        if (error)
                return error;
        if (!agbp)
                return -ENOMEM;

        cur = xfs_refcountbt_init_cursor(mp, NULL, agbp, agno, NULL);

        error = xfs_refcount_find_shared(cur, agbno, aglen, fbno, flen,
                        find_end_of_shared);

        xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);

        xfs_buf_relse(agbp);
        return error;
}

/*
 * Trim the mapping to the next block where there's a change in the
 * shared/unshared status.  More specifically, this means that we
 * find the lowest-numbered extent of shared blocks that coincides with
 * the given block mapping.  If the shared extent overlaps the start of
 * the mapping, trim the mapping to the end of the shared extent.  If
 * the shared region intersects the mapping, trim the mapping to the
 * start of the shared extent.  If there are no shared regions that
 * overlap, just return the original extent.
 */
int
xfs_reflink_trim_around_shared(
        struct xfs_inode        *ip,
        struct xfs_bmbt_irec    *irec,
        bool                    *shared,
        bool                    *trimmed)
{
        xfs_agnumber_t          agno;
        xfs_agblock_t           agbno;
        xfs_extlen_t            aglen;
        xfs_agblock_t           fbno;
        xfs_extlen_t            flen;
        int                     error = 0;

        /* Holes, unwritten, and delalloc extents cannot be shared */
        if (!xfs_is_reflink_inode(ip) ||
            ISUNWRITTEN(irec) ||
            irec->br_startblock == HOLESTARTBLOCK ||
            irec->br_startblock == DELAYSTARTBLOCK ||
            isnullstartblock(irec->br_startblock)) {
                *shared = false;
                return 0;
        }

        trace_xfs_reflink_trim_around_shared(ip, irec);

        agno = XFS_FSB_TO_AGNO(ip->i_mount, irec->br_startblock);
        agbno = XFS_FSB_TO_AGBNO(ip->i_mount, irec->br_startblock);
        aglen = irec->br_blockcount;

        error = xfs_reflink_find_shared(ip->i_mount, agno, agbno,
                        aglen, &fbno, &flen, true);
        if (error)
                return error;

        *shared = *trimmed = false;
        if (fbno == NULLAGBLOCK) {
                /* No shared blocks at all. */
                return 0;
        } else if (fbno == agbno) {
                /*
                 * The start of this extent is shared.  Truncate the
                 * mapping at the end of the shared region so that a
                 * subsequent iteration starts at the start of the
                 * unshared region.
                 */
                irec->br_blockcount = flen;
                *shared = true;
                if (flen != aglen)
                        *trimmed = true;
                return 0;
        } else {
                /*
                 * There's a shared extent midway through this extent.
                 * Truncate the mapping at the start of the shared
                 * extent so that a subsequent iteration starts at the
                 * start of the shared region.
                 */
                irec->br_blockcount = fbno - agbno;
                *trimmed = true;
                return 0;
        }
}

/*
 * Trim the passed in imap to the next shared/unshared extent boundary, and
 * if imap->br_startoff points to a shared extent reserve space for it in the
 * COW fork.  In this case *shared is set to true, else to false.
 *
 * Note that imap will always contain the block numbers for the existing blocks
 * in the data fork, as the upper layers need them for read-modify-write
 * operations.
 */
int
xfs_reflink_reserve_cow(
        struct xfs_inode        *ip,
        struct xfs_bmbt_irec    *imap,
        bool                    *shared)
{
        struct xfs_ifork        *ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        struct xfs_bmbt_irec    got;
        int                     error = 0;
        bool                    eof = false, trimmed;
        xfs_extnum_t            idx;

        /*
         * Search the COW fork extent list first.  This serves two purposes:
         * first this implement the speculative preallocation using cowextisze,
         * so that we also unshared block adjacent to shared blocks instead
         * of just the shared blocks themselves.  Second the lookup in the
         * extent list is generally faster than going out to the shared extent
         * tree.
         */

        if (!xfs_iext_lookup_extent(ip, ifp, imap->br_startoff, &idx, &got))
                eof = true;
        if (!eof && got.br_startoff <= imap->br_startoff) {
                trace_xfs_reflink_cow_found(ip, imap);
                xfs_trim_extent(imap, got.br_startoff, got.br_blockcount);

                *shared = true;
                return 0;
        }

        /* Trim the mapping to the nearest shared extent boundary. */
        error = xfs_reflink_trim_around_shared(ip, imap, shared, &trimmed);
        if (error)
                return error;

        /* Not shared?  Just report the (potentially capped) extent. */
        if (!*shared)
                return 0;

        /*
         * Fork all the shared blocks from our write offset until the end of
         * the extent.
         */
        error = xfs_qm_dqattach_locked(ip, 0);
        if (error)
                return error;

        error = xfs_bmapi_reserve_delalloc(ip, XFS_COW_FORK, imap->br_startoff,
                        imap->br_blockcount, 0, &got, &idx, eof);
        if (error == -ENOSPC || error == -EDQUOT)
                trace_xfs_reflink_cow_enospc(ip, imap);
        if (error)
                return error;

        trace_xfs_reflink_cow_alloc(ip, &got);
        return 0;
}

/* Convert part of an unwritten CoW extent to a real one. */
STATIC int
xfs_reflink_convert_cow_extent(
        struct xfs_inode                *ip,
        struct xfs_bmbt_irec            *imap,
        xfs_fileoff_t                   offset_fsb,
        xfs_filblks_t                   count_fsb,
        struct xfs_defer_ops            *dfops)
{
        struct xfs_bmbt_irec            irec = *imap;
        xfs_fsblock_t                   first_block = NULLFSBLOCK;
        int                             nimaps = 1;

        if (imap->br_state == XFS_EXT_NORM)
                return 0;

        xfs_trim_extent(&irec, offset_fsb, count_fsb);
        trace_xfs_reflink_convert_cow(ip, &irec);
        if (irec.br_blockcount == 0)
                return 0;
        return xfs_bmapi_write(NULL, ip, irec.br_startoff, irec.br_blockcount,
                        XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT, &first_block,
                        0, &irec, &nimaps, dfops);
}

/* Convert all of the unwritten CoW extents in a file's range to real ones. */
int
xfs_reflink_convert_cow(
        struct xfs_inode        *ip,
        xfs_off_t               offset,
        xfs_off_t               count)
{
        struct xfs_bmbt_irec    got;
        struct xfs_defer_ops    dfops;
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_ifork        *ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        xfs_fileoff_t           offset_fsb = XFS_B_TO_FSBT(mp, offset);
        xfs_fileoff_t           end_fsb = XFS_B_TO_FSB(mp, offset + count);
        xfs_extnum_t            idx;
        bool                    found;
        int                     error = 0;

        xfs_ilock(ip, XFS_ILOCK_EXCL);

        /* Convert all the extents to real from unwritten. */
        for (found = xfs_iext_lookup_extent(ip, ifp, offset_fsb, &idx, &got);
             found && got.br_startoff < end_fsb;
             found = xfs_iext_get_extent(ifp, ++idx, &got)) {
                error = xfs_reflink_convert_cow_extent(ip, &got, offset_fsb,
                                end_fsb - offset_fsb, &dfops);
                if (error)
                        break;
        }

        /* Finish up. */
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        return error;
}

/* Allocate all CoW reservations covering a range of blocks in a file. */
static int
__xfs_reflink_allocate_cow(
        struct xfs_inode        *ip,
        xfs_fileoff_t           *offset_fsb,
        xfs_fileoff_t           end_fsb)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_bmbt_irec    imap;
        struct xfs_defer_ops    dfops;
        struct xfs_trans        *tp;
        xfs_fsblock_t           first_block;
        int                     nimaps = 1, error;
        bool                    shared;

        xfs_defer_init(&dfops, &first_block);

        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0,
                        XFS_TRANS_RESERVE, &tp);
        if (error)
                return error;

        xfs_ilock(ip, XFS_ILOCK_EXCL);

        /* Read extent from the source file. */
        nimaps = 1;
        error = xfs_bmapi_read(ip, *offset_fsb, end_fsb - *offset_fsb,
                        &imap, &nimaps, 0);
        if (error)
                goto out_unlock;
        ASSERT(nimaps == 1);

        /* Make sure there's a CoW reservation for it. */
        error = xfs_reflink_reserve_cow(ip, &imap, &shared);
        if (error)
                goto out_trans_cancel;

        if (!shared) {
                *offset_fsb = imap.br_startoff + imap.br_blockcount;
                goto out_trans_cancel;
        }

        /* Allocate the entire reservation as unwritten blocks. */
        xfs_trans_ijoin(tp, ip, 0);
        error = xfs_bmapi_write(tp, ip, imap.br_startoff, imap.br_blockcount,
                        XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, &first_block,
                        XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK),
                        &imap, &nimaps, &dfops);
        if (error)
                goto out_trans_cancel;

        /* Finish up. */
        error = xfs_defer_finish(&tp, &dfops, NULL);
        if (error)
                goto out_trans_cancel;

        error = xfs_trans_commit(tp);

        *offset_fsb = imap.br_startoff + imap.br_blockcount;
out_unlock:
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        return error;
out_trans_cancel:
        xfs_defer_cancel(&dfops);
        xfs_trans_cancel(tp);
        goto out_unlock;
}

/* Allocate all CoW reservations covering a part of a file. */
int
xfs_reflink_allocate_cow_range(
        struct xfs_inode        *ip,
        xfs_off_t               offset,
        xfs_off_t               count)
{
        struct xfs_mount        *mp = ip->i_mount;
        xfs_fileoff_t           offset_fsb = XFS_B_TO_FSBT(mp, offset);
        xfs_fileoff_t           end_fsb = XFS_B_TO_FSB(mp, offset + count);
        int                     error;

        ASSERT(xfs_is_reflink_inode(ip));

        trace_xfs_reflink_allocate_cow_range(ip, offset, count);

        /*
         * Make sure that the dquots are there.
         */
        error = xfs_qm_dqattach(ip, 0);
        if (error)
                return error;

        while (offset_fsb < end_fsb) {
                error = __xfs_reflink_allocate_cow(ip, &offset_fsb, end_fsb);
                if (error) {
                        trace_xfs_reflink_allocate_cow_range_error(ip, error,
                                        _RET_IP_);
                        return error;
                }
        }

        /* Convert the CoW extents to regular. */
        return xfs_reflink_convert_cow(ip, offset, count);
}

/*
 * Find the CoW reservation (and whether or not it needs block allocation)
 * for a given byte offset of a file.
 */
bool
xfs_reflink_find_cow_mapping(
        struct xfs_inode                *ip,
        xfs_off_t                       offset,
        struct xfs_bmbt_irec            *imap,
        bool                            *need_alloc)
{
        struct xfs_bmbt_irec            irec;
        struct xfs_ifork                *ifp;
        struct xfs_bmbt_rec_host        *gotp;
        xfs_fileoff_t                   bno;
        xfs_extnum_t                    idx;

        ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL | XFS_ILOCK_SHARED));
        ASSERT(xfs_is_reflink_inode(ip));

        /* Find the extent in the CoW fork. */
        ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        bno = XFS_B_TO_FSBT(ip->i_mount, offset);
        gotp = xfs_iext_bno_to_ext(ifp, bno, &idx);
        if (!gotp)
                return false;

        xfs_bmbt_get_all(gotp, &irec);
        if (bno >= irec.br_startoff + irec.br_blockcount ||
            bno < irec.br_startoff)
                return false;

        trace_xfs_reflink_find_cow_mapping(ip, offset, 1, XFS_IO_OVERWRITE,
                        &irec);

        /* If it's still delalloc, we must allocate later. */
        *imap = irec;
        *need_alloc = !!(isnullstartblock(irec.br_startblock));

        return true;
}

/*
 * Trim an extent to end at the next CoW reservation past offset_fsb.
 */
int
xfs_reflink_trim_irec_to_next_cow(
        struct xfs_inode                *ip,
        xfs_fileoff_t                   offset_fsb,
        struct xfs_bmbt_irec            *imap)
{
        struct xfs_bmbt_irec            irec;
        struct xfs_ifork                *ifp;
        struct xfs_bmbt_rec_host        *gotp;
        xfs_extnum_t                    idx;

        if (!xfs_is_reflink_inode(ip))
                return 0;

        /* Find the extent in the CoW fork. */
        ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        gotp = xfs_iext_bno_to_ext(ifp, offset_fsb, &idx);
        if (!gotp)
                return 0;
        xfs_bmbt_get_all(gotp, &irec);

        /* This is the extent before; try sliding up one. */
        if (irec.br_startoff < offset_fsb) {
                idx++;
                if (idx >= xfs_iext_count(ifp))
                        return 0;
                gotp = xfs_iext_get_ext(ifp, idx);
                xfs_bmbt_get_all(gotp, &irec);
        }

        if (irec.br_startoff >= imap->br_startoff + imap->br_blockcount)
                return 0;

        imap->br_blockcount = irec.br_startoff - imap->br_startoff;
        trace_xfs_reflink_trim_irec(ip, imap);

        return 0;
}

/*
 * Cancel CoW reservations for some block range of an inode.
 *
 * If cancel_real is true this function cancels all COW fork extents for the
 * inode; if cancel_real is false, real extents are not cleared.
 */
int
xfs_reflink_cancel_cow_blocks(
        struct xfs_inode                *ip,
        struct xfs_trans                **tpp,
        xfs_fileoff_t                   offset_fsb,
        xfs_fileoff_t                   end_fsb,
        bool                            cancel_real)
{
        struct xfs_ifork                *ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        struct xfs_bmbt_irec            got, prev, del;
        xfs_extnum_t                    idx;
        xfs_fsblock_t                   firstfsb;
        struct xfs_defer_ops            dfops;
        int                             error = 0, eof = 0;

        if (!xfs_is_reflink_inode(ip))
                return 0;

        xfs_bmap_search_extents(ip, offset_fsb, XFS_COW_FORK, &eof, &idx,
                        &got, &prev);
        if (eof)
                return 0;

        while (got.br_startoff < end_fsb) {
                del = got;
                xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);
                trace_xfs_reflink_cancel_cow(ip, &del);

                if (isnullstartblock(del.br_startblock)) {
                        error = xfs_bmap_del_extent_delay(ip, XFS_COW_FORK,
                                        &idx, &got, &del);
                        if (error)
                                break;
                } else if (del.br_state == XFS_EXT_UNWRITTEN || cancel_real) {
                        xfs_trans_ijoin(*tpp, ip, 0);
                        xfs_defer_init(&dfops, &firstfsb);

                        /* Free the CoW orphan record. */
                        error = xfs_refcount_free_cow_extent(ip->i_mount,
                                        &dfops, del.br_startblock,
                                        del.br_blockcount);
                        if (error)
                                break;

                        xfs_bmap_add_free(ip->i_mount, &dfops,
                                        del.br_startblock, del.br_blockcount,
                                        NULL);

                        /* Update quota accounting */
                        xfs_trans_mod_dquot_byino(*tpp, ip, XFS_TRANS_DQ_BCOUNT,
                                        -(long)del.br_blockcount);

                        /* Roll the transaction */
                        error = xfs_defer_finish(tpp, &dfops, ip);
                        if (error) {
                                xfs_defer_cancel(&dfops);
                                break;
                        }

                        /* Remove the mapping from the CoW fork. */
                        xfs_bmap_del_extent_cow(ip, &idx, &got, &del);
                }

                if (++idx >= xfs_iext_count(ifp))
                        break;
                xfs_bmbt_get_all(xfs_iext_get_ext(ifp, idx), &got);
        }

        /* clear tag if cow fork is emptied */
        if (!ifp->if_bytes)
                xfs_inode_clear_cowblocks_tag(ip);

        return error;
}

/*
 * Cancel CoW reservations for some byte range of an inode.
 *
 * If cancel_real is true this function cancels all COW fork extents for the
 * inode; if cancel_real is false, real extents are not cleared.
 */
int
xfs_reflink_cancel_cow_range(
        struct xfs_inode        *ip,
        xfs_off_t               offset,
        xfs_off_t               count,
        bool                    cancel_real)
{
        struct xfs_trans        *tp;
        xfs_fileoff_t           offset_fsb;
        xfs_fileoff_t           end_fsb;
        int                     error;

        trace_xfs_reflink_cancel_cow_range(ip, offset, count);
        ASSERT(xfs_is_reflink_inode(ip));

        offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
        if (count == NULLFILEOFF)
                end_fsb = NULLFILEOFF;
        else
                end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);

        /* Start a rolling transaction to remove the mappings */
        error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
                        0, 0, 0, &tp);
        if (error)
                goto out;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        xfs_trans_ijoin(tp, ip, 0);

        /* Scrape out the old CoW reservations */
        error = xfs_reflink_cancel_cow_blocks(ip, &tp, offset_fsb, end_fsb,
                        cancel_real);
        if (error)
                goto out_cancel;

        error = xfs_trans_commit(tp);

        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        return error;

out_cancel:
        xfs_trans_cancel(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
        trace_xfs_reflink_cancel_cow_range_error(ip, error, _RET_IP_);
        return error;
}

/*
 * Remap parts of a file's data fork after a successful CoW.
 */
int
xfs_reflink_end_cow(
        struct xfs_inode                *ip,
        xfs_off_t                       offset,
        xfs_off_t                       count)
{
        struct xfs_ifork                *ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
        struct xfs_bmbt_irec            got, prev, del;
        struct xfs_trans                *tp;
        xfs_fileoff_t                   offset_fsb;
        xfs_fileoff_t                   end_fsb;
        xfs_fsblock_t                   firstfsb;
        struct xfs_defer_ops            dfops;
        int                             error, eof = 0;
        unsigned int                    resblks;
        xfs_filblks_t                   rlen;
        xfs_extnum_t                    idx;

        trace_xfs_reflink_end_cow(ip, offset, count);

        /* No COW extents?  That's easy! */
        if (ifp->if_bytes == 0)
                return 0;

        offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
        end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);

        /*
         * Start a rolling transaction to switch the mappings.  We're
         * unlikely ever to have to remap 16T worth of single-block
         * extents, so just cap the worst case extent count to 2^32-1.
         * Stick a warning in just in case, and avoid 64-bit division.
         */
        BUILD_BUG_ON(MAX_RW_COUNT > UINT_MAX);
        if (end_fsb - offset_fsb > UINT_MAX) {
                error = -EFSCORRUPTED;
                xfs_force_shutdown(ip->i_mount, SHUTDOWN_CORRUPT_INCORE);
                ASSERT(0);
                goto out;
        }
        resblks = XFS_NEXTENTADD_SPACE_RES(ip->i_mount,
                        (unsigned int)(end_fsb - offset_fsb),
                        XFS_DATA_FORK);
        error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
                        resblks, 0, 0, &tp);
        if (error)
                goto out;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        xfs_trans_ijoin(tp, ip, 0);

        xfs_bmap_search_extents(ip, end_fsb - 1, XFS_COW_FORK, &eof, &idx,
                        &got, &prev);

        /* If there is a hole at end_fsb - 1 go to the previous extent */
        if (eof || got.br_startoff > end_fsb) {
                /*
                 * In case of racing, overlapping AIO writes no COW extents
                 * might be left by the time I/O completes for the loser of
                 * the race.  In that case we are done.
                 */
                if (idx <= 0)
                        goto out_cancel;
                xfs_bmbt_get_all(xfs_iext_get_ext(ifp, --idx), &got);
        }

        /* Walk backwards until we're out of the I/O range... */
        while (got.br_startoff + got.br_blockcount > offset_fsb) {
                del = got;
                xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);

                /* Extent delete may have bumped idx forward */
                if (!del.br_blockcount) {
                        idx--;
                        goto next_extent;
                }

                ASSERT(!isnullstartblock(got.br_startblock));

                /*
                 * Don't remap unwritten extents; these are
                 * speculatively preallocated CoW extents that have been
                 * allocated but have not yet been involved in a write.
                 */
                if (got.br_state == XFS_EXT_UNWRITTEN) {
                        idx--;
                        goto next_extent;
                }

                /* Unmap the old blocks in the data fork. */
                xfs_defer_init(&dfops, &firstfsb);
                rlen = del.br_blockcount;
                error = __xfs_bunmapi(tp, ip, del.br_startoff, &rlen, 0, 1,
                                &firstfsb, &dfops);
                if (error)
                        goto out_defer;

                /* Trim the extent to whatever got unmapped. */
                if (rlen) {
                        xfs_trim_extent(&del, del.br_startoff + rlen,
                                del.br_blockcount - rlen);
                }
                trace_xfs_reflink_cow_remap(ip, &del);

                /* Free the CoW orphan record. */
                error = xfs_refcount_free_cow_extent(tp->t_mountp, &dfops,
                                del.br_startblock, del.br_blockcount);
                if (error)
                        goto out_defer;

                /* Map the new blocks into the data fork. */
                error = xfs_bmap_map_extent(tp->t_mountp, &dfops, ip, &del);
                if (error)
                        goto out_defer;

                /* Remove the mapping from the CoW fork. */
                xfs_bmap_del_extent_cow(ip, &idx, &got, &del);

                error = xfs_defer_finish(&tp, &dfops, ip);
                if (error)
                        goto out_defer;

next_extent:
                if (idx < 0)
                        break;
                xfs_bmbt_get_all(xfs_iext_get_ext(ifp, idx), &got);
        }

        error = xfs_trans_commit(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        if (error)
                goto out;
        return 0;

out_defer:
        xfs_defer_cancel(&dfops);
out_cancel:
        xfs_trans_cancel(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
        trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
        return error;
}

/*
 * Free leftover CoW reservations that didn't get cleaned out.
 */
int
xfs_reflink_recover_cow(
        struct xfs_mount        *mp)
{
        xfs_agnumber_t          agno;
        int                     error = 0;

        if (!xfs_sb_version_hasreflink(&mp->m_sb))
                return 0;

        for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
                error = xfs_refcount_recover_cow_leftovers(mp, agno);
                if (error)
                        break;
        }

        return error;
}

/*
 * Reflinking (Block) Ranges of Two Files Together
 *
 * First, ensure that the reflink flag is set on both inodes.  The flag is an
 * optimization to avoid unnecessary refcount btree lookups in the write path.
 *
 * Now we can iteratively remap the range of extents (and holes) in src to the
 * corresponding ranges in dest.  Let drange and srange denote the ranges of
 * logical blocks in dest and src touched by the reflink operation.
 *
 * While the length of drange is greater than zero,
 *    - Read src's bmbt at the start of srange ("imap")
 *    - If imap doesn't exist, make imap appear to start at the end of srange
 *      with zero length.
 *    - If imap starts before srange, advance imap to start at srange.
 *    - If imap goes beyond srange, truncate imap to end at the end of srange.
 *    - Punch (imap start - srange start + imap len) blocks from dest at
 *      offset (drange start).
 *    - If imap points to a real range of pblks,
 *         > Increase the refcount of the imap's pblks
 *         > Map imap's pblks into dest at the offset
 *           (drange start + imap start - srange start)
 *    - Advance drange and srange by (imap start - srange start + imap len)
 *
 * Finally, if the reflink made dest longer, update both the in-core and
 * on-disk file sizes.
 *
 * ASCII Art Demonstration:
 *
 * Let's say we want to reflink this source file:
 *
 * ----SSSSSSS-SSSSS----SSSSSS (src file)
 *   <-------------------->
 *
 * into this destination file:
 *
 * --DDDDDDDDDDDDDDDDDDD--DDD (dest file)
 *        <-------------------->
 * '-' means a hole, and 'S' and 'D' are written blocks in the src and dest.
 * Observe that the range has different logical offsets in either file.
 *
 * Consider that the first extent in the source file doesn't line up with our
 * reflink range.  Unmapping  and remapping are separate operations, so we can
 * unmap more blocks from the destination file than we remap.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *   <------->
 * --DDDDD---------DDDDD--DDD
 *        <------->
 *
 * Now remap the source extent into the destination file:
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *   <------->
 * --DDDDD--SSSSSSSDDDDD--DDD
 *        <------->
 *
 * Do likewise with the second hole and extent in our range.  Holes in the
 * unmap range don't affect our operation.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *            <---->
 * --DDDDD--SSSSSSS-SSSSS-DDD
 *                 <---->
 *
 * Finally, unmap and remap part of the third extent.  This will increase the
 * size of the destination file.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *                  <----->
 * --DDDDD--SSSSSSS-SSSSS----SSS
 *                       <----->
 *
 * Once we update the destination file's i_size, we're done.
 */

/*
 * Ensure the reflink bit is set in both inodes.
 */
STATIC int
xfs_reflink_set_inode_flag(
        struct xfs_inode        *src,
        struct xfs_inode        *dest)
{
        struct xfs_mount        *mp = src->i_mount;
        int                     error;
        struct xfs_trans        *tp;

        if (xfs_is_reflink_inode(src) && xfs_is_reflink_inode(dest))
                return 0;

        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
        if (error)
                goto out_error;

        /* Lock both files against IO */
        if (src->i_ino == dest->i_ino)
                xfs_ilock(src, XFS_ILOCK_EXCL);
        else
                xfs_lock_two_inodes(src, dest, XFS_ILOCK_EXCL);

        if (!xfs_is_reflink_inode(src)) {
                trace_xfs_reflink_set_inode_flag(src);
                xfs_trans_ijoin(tp, src, XFS_ILOCK_EXCL);
                src->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
                xfs_trans_log_inode(tp, src, XFS_ILOG_CORE);
                xfs_ifork_init_cow(src);
        } else
                xfs_iunlock(src, XFS_ILOCK_EXCL);

        if (src->i_ino == dest->i_ino)
                goto commit_flags;

        if (!xfs_is_reflink_inode(dest)) {
                trace_xfs_reflink_set_inode_flag(dest);
                xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
                dest->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
                xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
                xfs_ifork_init_cow(dest);
        } else
                xfs_iunlock(dest, XFS_ILOCK_EXCL);

commit_flags:
        error = xfs_trans_commit(tp);
        if (error)
                goto out_error;
        return error;

out_error:
        trace_xfs_reflink_set_inode_flag_error(dest, error, _RET_IP_);
        return error;
}

/*
 * Update destination inode size & cowextsize hint, if necessary.
 */
STATIC int
xfs_reflink_update_dest(
        struct xfs_inode        *dest,
        xfs_off_t               newlen,
        xfs_extlen_t            cowextsize,
        bool                    is_dedupe)
{
        struct xfs_mount        *mp = dest->i_mount;
        struct xfs_trans        *tp;
        int                     error;

        if (is_dedupe && newlen <= i_size_read(VFS_I(dest)) && cowextsize == 0)
                return 0;

        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
        if (error)
                goto out_error;

        xfs_ilock(dest, XFS_ILOCK_EXCL);
        xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);

        if (newlen > i_size_read(VFS_I(dest))) {
                trace_xfs_reflink_update_inode_size(dest, newlen);
                i_size_write(VFS_I(dest), newlen);
                dest->i_d.di_size = newlen;
        }

        if (cowextsize) {
                dest->i_d.di_cowextsize = cowextsize;
                dest->i_d.di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
        }

        if (!is_dedupe) {
                xfs_trans_ichgtime(tp, dest,
                                   XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
        }
        xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);

        error = xfs_trans_commit(tp);
        if (error)
                goto out_error;
        return error;

out_error:
        trace_xfs_reflink_update_inode_size_error(dest, error, _RET_IP_);
        return error;
}

/*
 * Do we have enough reserve in this AG to handle a reflink?  The refcount
 * btree already reserved all the space it needs, but the rmap btree can grow
 * infinitely, so we won't allow more reflinks when the AG is down to the
 * btree reserves.
 */
static int
xfs_reflink_ag_has_free_space(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno)
{
        struct xfs_perag        *pag;
        int                     error = 0;

        if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
                return 0;

        pag = xfs_perag_get(mp, agno);
        if (xfs_ag_resv_critical(pag, XFS_AG_RESV_AGFL) ||
            xfs_ag_resv_critical(pag, XFS_AG_RESV_METADATA))
                error = -ENOSPC;
        xfs_perag_put(pag);
        return error;
}

/*
 * Unmap a range of blocks from a file, then map other blocks into the hole.
 * The range to unmap is (destoff : destoff + srcioff + irec->br_blockcount).
 * The extent irec is mapped into dest at irec->br_startoff.
 */
STATIC int
xfs_reflink_remap_extent(
        struct xfs_inode        *ip,
        struct xfs_bmbt_irec    *irec,
        xfs_fileoff_t           destoff,
        xfs_off_t               new_isize)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_trans        *tp;
        xfs_fsblock_t           firstfsb;
        unsigned int            resblks;
        struct xfs_defer_ops    dfops;
        struct xfs_bmbt_irec    uirec;
        bool                    real_extent;
        xfs_filblks_t           rlen;
        xfs_filblks_t           unmap_len;
        xfs_off_t               newlen;
        int                     error;

        unmap_len = irec->br_startoff + irec->br_blockcount - destoff;
        trace_xfs_reflink_punch_range(ip, destoff, unmap_len);

        /* Only remap normal extents. */
        real_extent =  (irec->br_startblock != HOLESTARTBLOCK &&
                        irec->br_startblock != DELAYSTARTBLOCK &&
                        !ISUNWRITTEN(irec));

        /* No reflinking if we're low on space */
        if (real_extent) {
                error = xfs_reflink_ag_has_free_space(mp,
                                XFS_FSB_TO_AGNO(mp, irec->br_startblock));
                if (error)
                        goto out;
        }

        /* Start a rolling transaction to switch the mappings */
        resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
        if (error)
                goto out;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        xfs_trans_ijoin(tp, ip, 0);

        /* If we're not just clearing space, then do we have enough quota? */
        if (real_extent) {
                error = xfs_trans_reserve_quota_nblks(tp, ip,
                                irec->br_blockcount, 0, XFS_QMOPT_RES_REGBLKS);
                if (error)
                        goto out_cancel;
        }

        trace_xfs_reflink_remap(ip, irec->br_startoff,
                                irec->br_blockcount, irec->br_startblock);

        /* Unmap the old blocks in the data fork. */
        rlen = unmap_len;
        while (rlen) {
                xfs_defer_init(&dfops, &firstfsb);
                error = __xfs_bunmapi(tp, ip, destoff, &rlen, 0, 1,
                                &firstfsb, &dfops);
                if (error)
                        goto out_defer;

                /*
                 * Trim the extent to whatever got unmapped.
                 * Remember, bunmapi works backwards.
                 */
                uirec.br_startblock = irec->br_startblock + rlen;
                uirec.br_startoff = irec->br_startoff + rlen;
                uirec.br_blockcount = unmap_len - rlen;
                uirec.br_state = irec->br_state;
                unmap_len = rlen;

                /* If this isn't a real mapping, we're done. */
                if (!real_extent || uirec.br_blockcount == 0)
                        goto next_extent;

                trace_xfs_reflink_remap(ip, uirec.br_startoff,
                                uirec.br_blockcount, uirec.br_startblock);

                /* Update the refcount tree */
                error = xfs_refcount_increase_extent(mp, &dfops, &uirec);
                if (error)
                        goto out_defer;

                /* Map the new blocks into the data fork. */
                error = xfs_bmap_map_extent(mp, &dfops, ip, &uirec);
                if (error)
                        goto out_defer;

                /* Update quota accounting. */
                xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT,
                                uirec.br_blockcount);

                /* Update dest isize if needed. */
                newlen = XFS_FSB_TO_B(mp,
                                uirec.br_startoff + uirec.br_blockcount);
                newlen = min_t(xfs_off_t, newlen, new_isize);
                if (newlen > i_size_read(VFS_I(ip))) {
                        trace_xfs_reflink_update_inode_size(ip, newlen);
                        i_size_write(VFS_I(ip), newlen);
                        ip->i_d.di_size = newlen;
                        xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
                }

next_extent:
                /* Process all the deferred stuff. */
                error = xfs_defer_finish(&tp, &dfops, ip);
                if (error)
                        goto out_defer;
        }

        error = xfs_trans_commit(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        if (error)
                goto out;
        return 0;

out_defer:
        xfs_defer_cancel(&dfops);
out_cancel:
        xfs_trans_cancel(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
        trace_xfs_reflink_remap_extent_error(ip, error, _RET_IP_);
        return error;
}

/*
 * Iteratively remap one file's extents (and holes) to another's.
 */
STATIC int
xfs_reflink_remap_blocks(
        struct xfs_inode        *src,
        xfs_fileoff_t           srcoff,
        struct xfs_inode        *dest,
        xfs_fileoff_t           destoff,
        xfs_filblks_t           len,
        xfs_off_t               new_isize)
{
        struct xfs_bmbt_irec    imap;
        int                     nimaps;
        int                     error = 0;
        xfs_filblks_t           range_len;

        /* drange = (destoff, destoff + len); srange = (srcoff, srcoff + len) */
        while (len) {
                trace_xfs_reflink_remap_blocks_loop(src, srcoff, len,
                                dest, destoff);
                /* Read extent from the source file */
                nimaps = 1;
                xfs_ilock(src, XFS_ILOCK_EXCL);
                error = xfs_bmapi_read(src, srcoff, len, &imap, &nimaps, 0);
                xfs_iunlock(src, XFS_ILOCK_EXCL);
                if (error)
                        goto err;
                ASSERT(nimaps == 1);

                trace_xfs_reflink_remap_imap(src, srcoff, len, XFS_IO_OVERWRITE,
                                &imap);

                /* Translate imap into the destination file. */
                range_len = imap.br_startoff + imap.br_blockcount - srcoff;
                imap.br_startoff += destoff - srcoff;

                /* Clear dest from destoff to the end of imap and map it in. */
                error = xfs_reflink_remap_extent(dest, &imap, destoff,
                                new_isize);
                if (error)
                        goto err;

                if (fatal_signal_pending(current)) {
                        error = -EINTR;
                        goto err;
                }

                /* Advance drange/srange */
                srcoff += range_len;
                destoff += range_len;
                len -= range_len;
        }

        return 0;

err:
        trace_xfs_reflink_remap_blocks_error(dest, error, _RET_IP_);
        return error;
}

/*
 * Read a page's worth of file data into the page cache.  Return the page
 * locked.
 */
static struct page *
xfs_get_page(
        struct inode    *inode,
        xfs_off_t       offset)
{
        struct address_space    *mapping;
        struct page             *page;
        pgoff_t                 n;

        n = offset >> PAGE_SHIFT;
        mapping = inode->i_mapping;
        page = read_mapping_page(mapping, n, NULL);
        if (IS_ERR(page))
                return page;
        if (!PageUptodate(page)) {
                put_page(page);
                return ERR_PTR(-EIO);
        }
        lock_page(page);
        return page;
}

/*
 * Compare extents of two files to see if they are the same.
 */
static int
xfs_compare_extents(
        struct inode    *src,
        xfs_off_t       srcoff,
        struct inode    *dest,
        xfs_off_t       destoff,
        xfs_off_t       len,
        bool            *is_same)
{
        xfs_off_t       src_poff;
        xfs_off_t       dest_poff;
        void            *src_addr;
        void            *dest_addr;
        struct page     *src_page;
        struct page     *dest_page;
        xfs_off_t       cmp_len;
        bool            same;
        int             error;

        error = -EINVAL;
        same = true;
        while (len) {
                src_poff = srcoff & (PAGE_SIZE - 1);
                dest_poff = destoff & (PAGE_SIZE - 1);
                cmp_len = min(PAGE_SIZE - src_poff,
                              PAGE_SIZE - dest_poff);
                cmp_len = min(cmp_len, len);
                ASSERT(cmp_len > 0);

                trace_xfs_reflink_compare_extents(XFS_I(src), srcoff, cmp_len,
                                XFS_I(dest), destoff);

                src_page = xfs_get_page(src, srcoff);
                if (IS_ERR(src_page)) {
                        error = PTR_ERR(src_page);
                        goto out_error;
                }
                dest_page = xfs_get_page(dest, destoff);
                if (IS_ERR(dest_page)) {
                        error = PTR_ERR(dest_page);
                        unlock_page(src_page);
                        put_page(src_page);
                        goto out_error;
                }
                src_addr = kmap_atomic(src_page);
                dest_addr = kmap_atomic(dest_page);

                flush_dcache_page(src_page);
                flush_dcache_page(dest_page);

                if (memcmp(src_addr + src_poff, dest_addr + dest_poff, cmp_len))
                        same = false;

                kunmap_atomic(dest_addr);
                kunmap_atomic(src_addr);
                unlock_page(dest_page);
                unlock_page(src_page);
                put_page(dest_page);
                put_page(src_page);

                if (!same)
                        break;

                srcoff += cmp_len;
                destoff += cmp_len;
                len -= cmp_len;
        }

        *is_same = same;
        return 0;

out_error:
        trace_xfs_reflink_compare_extents_error(XFS_I(dest), error, _RET_IP_);
        return error;
}

/*
 * Link a range of blocks from one file to another.
 */
int
xfs_reflink_remap_range(
        struct file             *file_in,
        loff_t                  pos_in,
        struct file             *file_out,
        loff_t                  pos_out,
        u64                     len,
        bool                    is_dedupe)
{
        struct inode            *inode_in = file_inode(file_in);
        struct xfs_inode        *src = XFS_I(inode_in);
        struct inode            *inode_out = file_inode(file_out);
        struct xfs_inode        *dest = XFS_I(inode_out);
        struct xfs_mount        *mp = src->i_mount;
        loff_t                  bs = inode_out->i_sb->s_blocksize;
        bool                    same_inode = (inode_in == inode_out);
        xfs_fileoff_t           sfsbno, dfsbno;
        xfs_filblks_t           fsblen;
        xfs_extlen_t            cowextsize;
        loff_t                  isize;
        ssize_t                 ret;
        loff_t                  blen;

        if (!xfs_sb_version_hasreflink(&mp->m_sb))
                return -EOPNOTSUPP;

        if (XFS_FORCED_SHUTDOWN(mp))
                return -EIO;

        /* Lock both files against IO */
        if (same_inode) {
                xfs_ilock(src, XFS_IOLOCK_EXCL);
                xfs_ilock(src, XFS_MMAPLOCK_EXCL);
        } else {
                xfs_lock_two_inodes(src, dest, XFS_IOLOCK_EXCL);
                xfs_lock_two_inodes(src, dest, XFS_MMAPLOCK_EXCL);
        }

        /* Don't touch certain kinds of inodes */
        ret = -EPERM;
        if (IS_IMMUTABLE(inode_out))
                goto out_unlock;

        ret = -ETXTBSY;
        if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
                goto out_unlock;


        /* Don't reflink dirs, pipes, sockets... */
        ret = -EISDIR;
        if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
                goto out_unlock;
        ret = -EINVAL;
        if (S_ISFIFO(inode_in->i_mode) || S_ISFIFO(inode_out->i_mode))
                goto out_unlock;
        if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
                goto out_unlock;

        /* Don't reflink realtime inodes */
        if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
                goto out_unlock;

        /* Don't share DAX file data for now. */
        if (IS_DAX(inode_in) || IS_DAX(inode_out))
                goto out_unlock;

        /* Are we going all the way to the end? */
        isize = i_size_read(inode_in);
        if (isize == 0) {
                ret = 0;
                goto out_unlock;
        }

        /* Zero length dedupe exits immediately; reflink goes to EOF. */
        if (len == 0) {
                if (is_dedupe) {
                        ret = 0;
                        goto out_unlock;
                }
                len = isize - pos_in;
        }

        /* Ensure offsets don't wrap and the input is inside i_size */
        if (pos_in + len < pos_in || pos_out + len < pos_out ||
            pos_in + len > isize)
                goto out_unlock;

        /* Don't allow dedupe past EOF in the dest file */
        if (is_dedupe) {
                loff_t  disize;

                disize = i_size_read(inode_out);
                if (pos_out >= disize || pos_out + len > disize)
                        goto out_unlock;
        }

        /* If we're linking to EOF, continue to the block boundary. */
        if (pos_in + len == isize)
                blen = ALIGN(isize, bs) - pos_in;
        else
                blen = len;

        /* Only reflink if we're aligned to block boundaries */
        if (!IS_ALIGNED(pos_in, bs) || !IS_ALIGNED(pos_in + blen, bs) ||
            !IS_ALIGNED(pos_out, bs) || !IS_ALIGNED(pos_out + blen, bs))
                goto out_unlock;

        /* Don't allow overlapped reflink within the same file */
        if (same_inode) {
                if (pos_out + blen > pos_in && pos_out < pos_in + blen)
                        goto out_unlock;
        }

        /* Wait for the completion of any pending IOs on both files */
        inode_dio_wait(inode_in);
        if (!same_inode)
                inode_dio_wait(inode_out);

        ret = filemap_write_and_wait_range(inode_in->i_mapping,
                        pos_in, pos_in + len - 1);
        if (ret)
                goto out_unlock;

        ret = filemap_write_and_wait_range(inode_out->i_mapping,
                        pos_out, pos_out + len - 1);
        if (ret)
                goto out_unlock;

        trace_xfs_reflink_remap_range(src, pos_in, len, dest, pos_out);

        /*
         * Check that the extents are the same.
         */
        if (is_dedupe) {
                bool            is_same = false;

                ret = xfs_compare_extents(inode_in, pos_in, inode_out, pos_out,
                                len, &is_same);
                if (ret)
                        goto out_unlock;
                if (!is_same) {
                        ret = -EBADE;
                        goto out_unlock;
                }
        }

        ret = xfs_reflink_set_inode_flag(src, dest);
        if (ret)
                goto out_unlock;

        /*
         * Invalidate the page cache so that we can clear any CoW mappings
         * in the destination file.
         */
        truncate_inode_pages_range(&inode_out->i_data, pos_out,
                                   PAGE_ALIGN(pos_out + len) - 1);

        dfsbno = XFS_B_TO_FSBT(mp, pos_out);
        sfsbno = XFS_B_TO_FSBT(mp, pos_in);
        fsblen = XFS_B_TO_FSB(mp, len);
        ret = xfs_reflink_remap_blocks(src, sfsbno, dest, dfsbno, fsblen,
                        pos_out + len);
        if (ret)
                goto out_unlock;

        /*
         * Carry the cowextsize hint from src to dest if we're sharing the
         * entire source file to the entire destination file, the source file
         * has a cowextsize hint, and the destination file does not.
         */
        cowextsize = 0;
        if (pos_in == 0 && len == i_size_read(inode_in) &&
            (src->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE) &&
            pos_out == 0 && len >= i_size_read(inode_out) &&
            !(dest->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE))
                cowextsize = src->i_d.di_cowextsize;

        ret = xfs_reflink_update_dest(dest, pos_out + len, cowextsize,
                        is_dedupe);

out_unlock:
        xfs_iunlock(src, XFS_MMAPLOCK_EXCL);
        xfs_iunlock(src, XFS_IOLOCK_EXCL);
        if (src->i_ino != dest->i_ino) {
                xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
                xfs_iunlock(dest, XFS_IOLOCK_EXCL);
        }
        if (ret)
                trace_xfs_reflink_remap_range_error(dest, ret, _RET_IP_);
        return ret;
}

/*
 * The user wants to preemptively CoW all shared blocks in this file,
 * which enables us to turn off the reflink flag.  Iterate all
 * extents which are not prealloc/delalloc to see which ranges are
 * mentioned in the refcount tree, then read those blocks into the
 * pagecache, dirty them, fsync them back out, and then we can update
 * the inode flag.  What happens if we run out of memory? :)
 */
STATIC int
xfs_reflink_dirty_extents(
        struct xfs_inode        *ip,
        xfs_fileoff_t           fbno,
        xfs_filblks_t           end,
        xfs_off_t               isize)
{
        struct xfs_mount        *mp = ip->i_mount;
        xfs_agnumber_t          agno;
        xfs_agblock_t           agbno;
        xfs_extlen_t            aglen;
        xfs_agblock_t           rbno;
        xfs_extlen_t            rlen;
        xfs_off_t               fpos;
        xfs_off_t               flen;
        struct xfs_bmbt_irec    map[2];
        int                     nmaps;
        int                     error = 0;

        while (end - fbno > 0) {
                nmaps = 1;
                /*
                 * Look for extents in the file.  Skip holes, delalloc, or
                 * unwritten extents; they can't be reflinked.
                 */
                error = xfs_bmapi_read(ip, fbno, end - fbno, map, &nmaps, 0);
                if (error)
                        goto out;
                if (nmaps == 0)
                        break;
                if (map[0].br_startblock == HOLESTARTBLOCK ||
                    map[0].br_startblock == DELAYSTARTBLOCK ||
                    ISUNWRITTEN(&map[0]))
                        goto next;

                map[1] = map[0];
                while (map[1].br_blockcount) {
                        agno = XFS_FSB_TO_AGNO(mp, map[1].br_startblock);
                        agbno = XFS_FSB_TO_AGBNO(mp, map[1].br_startblock);
                        aglen = map[1].br_blockcount;

                        error = xfs_reflink_find_shared(mp, agno, agbno, aglen,
                                        &rbno, &rlen, true);
                        if (error)
                                goto out;
                        if (rbno == NULLAGBLOCK)
                                break;

                        /* Dirty the pages */
                        xfs_iunlock(ip, XFS_ILOCK_EXCL);
                        fpos = XFS_FSB_TO_B(mp, map[1].br_startoff +
                                        (rbno - agbno));
                        flen = XFS_FSB_TO_B(mp, rlen);
                        if (fpos + flen > isize)
                                flen = isize - fpos;
                        error = iomap_file_dirty(VFS_I(ip), fpos, flen,
                                        &xfs_iomap_ops);
                        xfs_ilock(ip, XFS_ILOCK_EXCL);
                        if (error)
                                goto out;

                        map[1].br_blockcount -= (rbno - agbno + rlen);
                        map[1].br_startoff += (rbno - agbno + rlen);
                        map[1].br_startblock += (rbno - agbno + rlen);
                }

next:
                fbno = map[0].br_startoff + map[0].br_blockcount;
        }
out:
        return error;
}

/* Clear the inode reflink flag if there are no shared extents. */
int
xfs_reflink_clear_inode_flag(
        struct xfs_inode        *ip,
        struct xfs_trans        **tpp)
{
        struct xfs_mount        *mp = ip->i_mount;
        xfs_fileoff_t           fbno;
        xfs_filblks_t           end;
        xfs_agnumber_t          agno;
        xfs_agblock_t           agbno;
        xfs_extlen_t            aglen;
        xfs_agblock_t           rbno;
        xfs_extlen_t            rlen;
        struct xfs_bmbt_irec    map;
        int                     nmaps;
        int                     error = 0;

        ASSERT(xfs_is_reflink_inode(ip));

        fbno = 0;
        end = XFS_B_TO_FSB(mp, i_size_read(VFS_I(ip)));
        while (end - fbno > 0) {
                nmaps = 1;
                /*
                 * Look for extents in the file.  Skip holes, delalloc, or
                 * unwritten extents; they can't be reflinked.
                 */
                error = xfs_bmapi_read(ip, fbno, end - fbno, &map, &nmaps, 0);
                if (error)
                        return error;
                if (nmaps == 0)
                        break;
                if (map.br_startblock == HOLESTARTBLOCK ||
                    map.br_startblock == DELAYSTARTBLOCK ||
                    ISUNWRITTEN(&map))
                        goto next;

                agno = XFS_FSB_TO_AGNO(mp, map.br_startblock);
                agbno = XFS_FSB_TO_AGBNO(mp, map.br_startblock);
                aglen = map.br_blockcount;

                error = xfs_reflink_find_shared(mp, agno, agbno, aglen,
                                &rbno, &rlen, false);
                if (error)
                        return error;
                /* Is there still a shared block here? */
                if (rbno != NULLAGBLOCK)
                        return 0;
next:
                fbno = map.br_startoff + map.br_blockcount;
        }

        /*
         * We didn't find any shared blocks so turn off the reflink flag.
         * First, get rid of any leftover CoW mappings.
         */
        error = xfs_reflink_cancel_cow_blocks(ip, tpp, 0, NULLFILEOFF, true);
        if (error)
                return error;

        /* Clear the inode flag. */
        trace_xfs_reflink_unset_inode_flag(ip);
        ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
        xfs_inode_clear_cowblocks_tag(ip);
        xfs_trans_ijoin(*tpp, ip, 0);
        xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);

        return error;
}

/*
 * Clear the inode reflink flag if there are no shared extents and the size
 * hasn't changed.
 */
STATIC int
xfs_reflink_try_clear_inode_flag(
        struct xfs_inode        *ip)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_trans        *tp;
        int                     error = 0;

        /* Start a rolling transaction to remove the mappings */
        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
        if (error)
                return error;

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        xfs_trans_ijoin(tp, ip, 0);

        error = xfs_reflink_clear_inode_flag(ip, &tp);
        if (error)
                goto cancel;

        error = xfs_trans_commit(tp);
        if (error)
                goto out;

        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        return 0;
cancel:
        xfs_trans_cancel(tp);
out:
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        return error;
}

/*
 * Pre-COW all shared blocks within a given byte range of a file and turn off
 * the reflink flag if we unshare all of the file's blocks.
 */
int
xfs_reflink_unshare(
        struct xfs_inode        *ip,
        xfs_off_t               offset,
        xfs_off_t               len)
{
        struct xfs_mount        *mp = ip->i_mount;
        xfs_fileoff_t           fbno;
        xfs_filblks_t           end;
        xfs_off_t               isize;
        int                     error;

        if (!xfs_is_reflink_inode(ip))
                return 0;

        trace_xfs_reflink_unshare(ip, offset, len);

        inode_dio_wait(VFS_I(ip));

        /* Try to CoW the selected ranges */
        xfs_ilock(ip, XFS_ILOCK_EXCL);
        fbno = XFS_B_TO_FSBT(mp, offset);
        isize = i_size_read(VFS_I(ip));
        end = XFS_B_TO_FSB(mp, offset + len);
        error = xfs_reflink_dirty_extents(ip, fbno, end, isize);
        if (error)
                goto out_unlock;
        xfs_iunlock(ip, XFS_ILOCK_EXCL);

        /* Wait for the IO to finish */
        error = filemap_write_and_wait(VFS_I(ip)->i_mapping);
        if (error)
                goto out;

        /* Turn off the reflink flag if possible. */
        error = xfs_reflink_try_clear_inode_flag(ip);
        if (error)
                goto out;

        return 0;

out_unlock:
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
        trace_xfs_reflink_unshare_error(ip, error, _RET_IP_);
        return error;
}